Polymer microgels that take careful tuning

Altering nanoparticle synthesis for a range of microgel applications.

A team of chemists from the University of Toronto, Canada, has developed a polymer microgel that can act as a highly tuneable reactor for the synthesis of semiconductor, metal and magnetic nanoparticles. By changing the reaction conditions and composition of the microgel templates, the researchers discovered they could finely control the size, concentration, distribution, and therefore behaviour of the nanoparticles.

The development of microscopic spheres coated or doped with various nanoparticles has been an active area of nanotechnology research over the past few years and such spheres have already been used for biological labelling and for the construction of photonic materials.

Scientists have, however, come up against a number of problems in creating nanoparticle-containing microspheres. If the nanoparticles are formed before being added to the microspheres then it is often difficult to achieve high enough concentrations, while if they are constructed within the microsphere it can be difficult to control their size, shape and quality. The polymer microgel developed by the Canadian chemists is able to overcome many of these problems.

The microgel is formed from poly( N-isopropyl acrylamide-acrylic acid-2-hydroxy-ethyl acrylate) crosslinked with N, N’-methylene bisacrylamide. The chemists synthesise nanoparticles within the polymer microgel by deprotonating the carboxyl groups on the acrylic acid section of the polymer and then incorporating precursor cations via ion exchange. These cations then act as seeds for the build up of the nanoparticles.The advantage of this microgel is that the size and concentration of the nanoparticles can be controlled by changing the amount of acrylic acid and 2-hydroxy-ethyl acrylate in the polymer and by increasing the pH during the first stage of nanoparticle synthesis. This means that the chemists can finely tune the synthesis of the nanoparticles and thereby create microgels that exhibit a variety of different behaviours.

To demonstrate their potential, the chemists developed polymer microgels that contained nanoparticles made of silver, the semiconductor CdS, and the magnetic compound Fe ₃O ₄. They then showed that they could induce the CdS nanoparticles to emit light over the entire visible spectrum and could control the magnetic properties of the Fe ₃O ₄ nanoparticles.

Jon Evans